A multi-locus molecular timescale for the origin and diversification of eels (Order: Anguilliformes)

Anguilliformes are an ecologically diverse group of predominantly marine fishes whose members are easily recognized by their extremely elongate bodies, and universal lack of pelvic fins. A number of recent studies based on mitochondrial loci, including full mitogenomes, have called into question the monophyly of both the Anguilliformes, which appear to be paraphyletic without the inclusion of the Saccopharyngiformes (gulper eels and allies), as well as that of some traditional eel families (e.g., Congridae, Serrivomeridae). To date, however, no study has attempted to investigate anguilliform interrelationships using nuclear loci. Here we present the result of a new phylogenetic study based on five markers (the nuclear loci Early Growth Hormone 3, Myosin Heavy Polypeptide 6 and Recombinase Activating gene 1, as well as the mitochondrial genes Cytochrome b and Cytochrome Oxydase I). We sampled 113 species of anguilliforms and saccopharyngiforms, plus four elopomorph outgroups. We added another 31 taxa for which sequences were available in GenBank, bringing the total number of taxa in our study to 148, doubling the number of anguilliform taxa for any study published to date and representing 19 of the 20 extant families of anguilliforms and saccopharyngiforms. Maximum likelihood analysis of the new dataset reveals that saccopharyngiform eels are deeply nested within the anguilliforms, and supports the non-monophyly of Congridae and Nettastomatidae, as well as that of Derichthyidae and Chlopsidae. The recently described Protanguilla is shown to be the sister group of the Synaphobranchidae, instead of the sister group to all other anguilliforms. The molecular phylogeny, time-calibrated using a Bayesian relaxed clock approach and 7 fossil calibration points, reveals a late Cretaceous origin of this expanded anguilliform clade (stem age ~116 Ma, crown age ~99 Ma). Most major (family level) lineages originated between the end of the Cretaceous and early Eocene, suggesting that anguilliform radiation may have been facilitated by the recovery of marine ecosystems following the KP extinction.